Superheterodyne receiver



1937- K. POSTHUMUS ET AL 2,095,035

SUPERHETERODYNE RECEIVER Filed Dec. 18, 1935 2 Sheets-Sheet 1 &

INVENTOR AL/MS POST/90410.5

77/600 BUS WEXEBS ATTORNEY Oct; 5, 1937. K. POSTHUMUS ET AL 2,095,035

SUPERHETERODYNE RECE I VER Filed Dec. 18, 1933 2 Sheets-Sheet 2 C3 INVENTOR l M445 Poms 0,410.5

27/5000 0 .zwerms BY ATTORNEY Patented Oct. 5, 1937 UNITD STATES FATE OFFICE SUPEBHETERODYNE RECEIVER aware Application December 18, 1933, Serial No. 702,912 In Germany January 2, 1933 1 Claim.

The present invention relates to oscillator circuits for superheterodyne receivers, and particularly to oscillator circuits for superheterodyne receivers for obtaining a constant intermediate frequency. a

In the usual superheterodyne receivers use is mostly made of a local oscillator circuit consisting of two parallel branches comprising a series and parallel connection of condensers and a self-inductance respectively, as is shown in Fig. 1. The tuning device of the local oscillator circuit is preferably mechanically coupled with the tuning device of the circuits tuned to the signal to be received in order to obtain the simplest possible adjustment of the receiving set. Such tuning has the drawback that the difference between the resonance frequencies of the oscillator circuit and of the circuit tuned to the signal to be received is for all the frequencies not equal to the intermediate frequency. Figure 2 shows the difference of these resonance frequencies for the frequency range to be received, said difference be ing designated by the difference frequency V V1 is the lowest, V2 the highest frequency to be received, and Vm is the intermediate frequency to which the intermediate frequency circuits are tuned. The elements of the circuits are preferably so taken that for V3 and for V4 the differences between V and Vm are equal in absolute value.

If V2=3V1 this difference is for V3, and for V4 about 1.5% of Vm. For receiving, for example, the frequency V3, the tuning members are adjusted in such manner that the oscillator frequency amounts to V3-1-Vm.

The tuning is substantially determined by the most selective element of the receiving appara' tus, in the present case by the intermediate frequency circuits. In this case the frequency V3 to be received differs by from the resonance frequency of the high-frequency circuits as is shown in Figure 3. The curve a represents the resonance curve of the high frequency circuits where the resonance frequency is V1. V3 is the frequency to be received, and V3+Vm is the oscillator frequency, the difference between V3+Vm and V1 being V T00 large a difference between V and Vm results in a reduction of the amplification and in distor-.

tion. If the maximum difference of 1.5 KC/seo. is allowed, the maximum intermediate frequency which may be employed amounts to 100 KC/sec. A higher intermediate frequency afiords, howquency part the number of circuits may be reduced.

The object of the present invention is to form the local oscillator circuit in such manner that in all the positions of the tuning members the difference between the resonance frequencies of the circuits tuned to the frequency to be received and of the oscillator, circuit is as much as possible equal to the intermediate frequency, and 5 5 more particularly that with the same intermediate frequency the maximum value of this difference is smaller than in the usual circuit-arrangement, and that consequently with a constant maximum difference between V and Vm the in- :20 termediate frequency Vm may be higher.

In the drawings:-

Fig. l is a circuit arrangement of a conventional superheterodyne receiver showing the prior art construction of the local oscillator, 25

Figs. 2 and 3 show characteristics of the receiver of Fig. 1,

Fig. 4 shows one form. of the invention applied to the local oscillator network of the receiver in Fig. 1, 30

Fig. 5 illustrates a characteristic of the circuit of Fig. 4,

Fig. 6 shows another modification, and Fig. 7 illustrates the characteristic thereof,

Fig. 8 shows a modification of the arrangement :35 of Fig, 6, Fig. '7 illustrating its characteristic,

Fig. 9 shows another modification, Fig. 10 illustrating its characteristic,

Figs. 11, 12 and 13 show further modifications,

Fig. 14 shows still another modification, Fig. 15 40 depicting its characteristic.

In the present invention there is added to the circuit-arrangement according to' Figure 1 one or more elements of which at least one is a resistance. The condenser C2 in Figure 1 operates 45 we ha've i V equation, '3

ticnalincrease desired at the low frequencyend simpler manner byconnectingas shown in Fig.

- the condenser Cz'andthe resistance R1 amounts iwu. i

fori cronvenience, shallibereferred to as r; 'In this 1i .R w c is the fractional increaseli Knowing the fracof the band of frequencies overthe high frequency shape'showninFigure'Z;

'end-in orderto maintain, .tracking, it remains only'toiindjwhat value R1 will" make the ex- ,pression V V i (thefractionalincrease) have the desired-value. Since V Rlzwgclz' V V aandj r' both represent the same thing, we have' Rim-Cy;

'Theeffect of the resistance R1 is consequently an increase of'the virtual resistanceof the circuit (which with an oscillator circuitis no preponderantfdrawback), and an increase of the virtual ca pacity in the case of a decreasing frequency.

The, result aimed at may consequently be obtai'nedgby giving the resistance R1 such a'value so that for the. frequency V1 thevalue ni w cz'? is no longer very large relatively to 1 e.' g. fl).

'Flgureifi shows the difference frequency as Ja function of the 'freq'uency,to be received 'with this circuit-arrangement:

I tween I the difference frequency and the intermediate frequen'cyiislinthis case about 0.37% of The largest difference be-f the intermediate frequency; 7

In a similar mannerit may 'be.,-e rplained that withia circuit-arrangement'as' shown in Figure 6 in which a'resista'nce R2 is connected in series with a condenser C3, the difference frequencyplotted as a function of the'frequency to be received has the a Figure 8 represents a modified form of execu-' tion of the circuitgarrangement}according to "-Figure fi, in which the branch RgCs isiconnected "'injparallel with" L1.' For, this circuit-arrangei I 'mentthe dii ference frequency is also represented by Figure 7.1 i

Another circuitearrangementaccording to the c iinvention'is shown in Figure 9. i In parallel with Z impedance.

branch consisting of the'series' connection of a 're-j sistance R3 and a circuit formed by a self inductance L2, a resistance'Ri and a capacity C4; This circuit LzC i is tuned to the frequency V5 "(Figure .'2). For this frequencyfthis circuit has a real The natural frequency of the original circuit consisting of L1, 01,02 and'Ca' is not appreciably influenced .by' the branch added .in

accordance with the invention. For the fre-l quencies V1 and. V2 the impedance of the circuit formed by'Lz and C4 is small The impedanceof the circuitformed by La and C4 is small. The ir'npedance of the branch R3, L2, Cialso becomes a1-. a "151 quency. For frequencies slightlyglower than V5 This equationstates in mathematical language 'thatjthe effective capacity C is equal to the actual condenser capacity 0?, plusC times a; 'frac tionali( or percentage) increase; which fraction, 7

'most' real, and hardlyacts on the oscillator free the impedance of the circuit L 2C4 is'inductive and increases'the oscillator, frequency] For; frequencies slightly higher than -V 5 the impedance of the circuit 112C415 a capacitative one and consequently'decreases the oscillator frequency. j

circuit LzCrxshould not become; too large, the

damping of this circuit must be ratherflarge; r

I This may be obtained' by adding a resistance a "or by winding 'theicoil Lz of resistance wire, q i r .30 -i The circuit arrangements according tofFigures 11, 12 and "13'dua l1y correspond to those of the 7 Figures 4,6,9 respectively. Fortwo dual circuit 7 r i 7 arrangements the difference frequency is equal.

Some of the circuit arrangements shown may' also be combined. Figure 14 represents a combination of the circuit arrangements of Figures 4,;

hand 9; Figure 15 shows the, variation difference frequency irr'this case,

The above-described circuit arrangements may still be extended by adding to the oscillator circuit variousel'ements among which there are also resistances. V For practica howe'ver, the cirof the cuit-arrangements described give as a rule asufficiently constant different frequency; 7

Whilewe have indicated and described severa many modifications may be made without depart? in the appended claim.

What is claimed-isz- V r In combination, in a heterodynereceiver,a V V first detector having a means tunable over. a

ers in series with each other and in parallel with the othersaid condenser, the valueof said resistance measured in ohms being equal to a num-f ber of the order of twice the reactance vof .thej' otherconderiserat the lower *end'of the frequency v 345 i 7 systems for carrying our invention into effect, it

' will be apparent to one skilled in the art thatour invention is by no means limited to the particular organizations shown and described, but that j 1 ing from the scope of our invention, as setforth.

range, and means for uni-controllingsaid tunable means and said'variable condenser.

KLAAS POSTHUMUS.

rnnonoaus JOSEPHUS WEYEQRS." V v 

